“The assault has begun,” said Ukraine defense ministry spokesman Vladislav Seleznyov through a social media account on Thursday. The Ukraine defense ministry went on to say that 20 pro-Russian gunmen stormed the Ukrainian warship, the Ternopil, in the port of Sevastopol in Crimea, Agence France Presse reported.

The storming of the Ternopil comes on the same day that President Obama, speaking on on the South Lawn of the White House, said: “Russia must know that further escalation will only isolate it further from the international community.”

On Thursday, the president announced a new round of sanctions against Russia for the nation’s invasion of the Crimea region of Ukraine.